The present invention is generally directed to processes for ink compositions; and more specifically the present invention is directed to improved processes for formulating ink compositions useful in ink jet printing apparatuses especially those commercially available such as, for example, the Diablo C-150. Accordingly, in one embodiment of the present invention there is provided a process for ink compositions wherein an oil soluble dye is entrained or trapped in a polymer matrix by affecting the dissolution of a polymer and a dye in a solvent phase; dispersing the mixture formulated in water; permitting the formation of an oil phase, and a water phase; and thereafter removing the solvent thereby enabling discrete dye polymer particles in water. The aforementioned particles when jetted onto a paper substrate possess improved waterfastness, and a decrease in feathering or wicking of the ink composition. Also, these discrete particle compositions which can be stabilized by various surfactants are very useful as marking particles in known ink jet printing processes.
Compositions, especially those with water soluble dyes, for ink jet printing processes are well known. There is thus disclosed, for example in U.S. Pat. No. 3,846,141, an ink jet printing composition comprised of an aqueous solution of a water-soluble dye and a humectant material formed from a mixture of a lower alkoxy triglycol, and at least one other compound selected from the group consisting of a polyethylene glycol, a lower alkyl ether of diethylene glycol, and glycerol. According to the disclosure of this patent, the printing inks illustrated are of a viscosity that is subjected to little variation with use as water is lost by evaporation during recirculation of the ink composition through the jet printer. Moreover, apparently the humectant system disclosed in this patent substantially prevents or minimizes tip drying of the printing ink in the orifice or nozzle during down time of the printer, such as when the printer is rendered inoperative. Also, it is indicated in this patent that the basic imaging technique in jet printing involves the use of one or more ink jet assemblies connected at a pressurized source of ink. Each individual ink jet includes a very small orifice, usually of a diameter of 0.0024 inches, through which is propelled the ink by a magneto restrictive piezoelectric means resulting in a continuous stream of uniform droplets of ink at a rate of 33 to 75 kilohertz. This stream of droplets is desirably directed onto the surface of a moving web of, for example paper; and is controlled to form printed characters in response to video signals derived from an electronic character generator, and in response to an electrostatic deflection system.
Also, there are disclosed in U.S. Pat. No. 4,279,653 ink jet compositions with water-soluble wetting gents, a water-soluble dye and an oxygen absorber. Similarly, U.S. Pat. No. 4,196,007 describes an ink jet printing composition consisting of an aqueous solution of a water-soluble dye and a humectant with at least one water-soluble unsaturated compound. Other prior are disclosing aqueous inks for ink jet printing, and processes of the preparation thereof are U.S. Pat. Nos. 4,101,329; 4,290,072 and 4,299,630.
Ink jet compositions can be prepared by a number of known methods. Generally, these methods involve dissolving the various dyes, humectants, viscosity control agents, paper fixing additives, surface tension control additives, biocides and anti-oxidants in a known volume of water, followed by adjusting the pH and concentration of the solution to desirable levels. In those situations wherein the dyes selected are not water-soluble, the inks are prepared by standard known milling processes. However, the dye dispersions are generally not sufficiently stable, and accordingly when incorporated into a printing machine, the ink particles tend to agglomerate resulting in the clogging of the small nozzles present in the ink jet devices. One of the important objectives of the present invention resides in the preparation of stabilized discrete particles of a uniform, less than 0.5 microns, average diameter, for example, thus preventing the undesirable agglomeration of these particles.
Moreover, processes for dispersing liquids by the use of ultrasonic vibrations is generally known. For example, there is described in U.S. Pat. No. 3,361,680 processes for dispersing one liquid into another by the use of ultrasonic vibrations. More specifically, there is disclosed in this patent a process for dispersing one liquid into a second liquid immiscible therewith by subjecting the mixture to ultrasonic vibrations wherein there is added to the first liquid an inert liquid, followed by heating the mixture. According to the teachings of this patent, one advantage of using ultrasonic vibrations is to obtain smaller size dispersed phase particles, that is, more stable dispersions.
Additionally, polymer particles can be prepared by known suspension polymerization and emulsion polymerization processes. In suspension polymerization, there is selected a monomer-soluble free radical initiator dissolved in a large size, approaching 40 to 300 microns in diameter, dispersion droplet with stabilization or the dispersion being accomplished with a dispersant or suspending agent other than a surfactant. With emulsion polymerization, water-soluble initiators and surfactants are used for the purpose of stabilizing the polymerized monomer dispersions. In contrast, in microsuspension polymerization; and particularly, with the preparation of polymer microlatices, there are selected surfactants, monomer-soluble initiators, and a water-soluble free radical inhibitors. Polymer particles of the desired size are formed by subjecting the mixture of water, monomer and surfactant to intense shear whereby the results monomer droplets of a size corresponding to that of the polymer desired. Specifically, with microsuspension polymerization, a monomer, a dissolved initiator, and water containing a specific emulsifier are homogenized in a colloid mill into very small droplets of a diameter of from 0.2 to 1.0 microns prior to polymerization. Subsequently, these droplets are polymerized enabling polymer particles with a diameter of from about 0.4 to 2 microns. Also, microsuspension, polymerization can be selected for the preparation of polyvinyl chloride resins suitable for conversion to plastisols.
Also, there is illustrated in U.S. Ser. No. 722,100, now U.S. Pat. No. 4,652,508 entitled Toner Composition and Dispersion Polymerization Process, the disclosure of which is totally incorporated herein by reference, a process for the preparation of particles for ink jet printing which comprises (1) providing a monomer having dissoled therein oil-soluble dyes; (2) mixing with the resulting monomer particles polymer initiator substances; (3) mechanically agitating the resulting solution; (4) subsequently adding thereto a solution of water and surfactant agents; (5) subjecting the resulting solution to ultrasound vibrations, followed by heating at a polymerization temperature of from about 50.degree. C. to about 100.degree. C., resulting in polymer particles of a diameter of from about 0.03 microns to about 2.0 microns and containing therein oil-soluble dyes, stabilized by surfactant. With the process of the present invention, there is no polymer formation as a preformed polymer is selected for particle fabrication. Further, the dyes utilized for the process of the present invention as they retain their color characteristics are not subjected to adverse oxidation reactions by the free radical initiator. In contrast with the dyes used, for example in microsuspension polymerizations, changes in the dye color can easily result.
There is also disclosed in U.S. Pat. No. 4,246,154 a process for permitting the formulation of ink jet compositions from vinyl polymer latices by a dye imbibition technique. The aforementioned anionically stabilized latices, which are obtained by emulsion polymerization, are colored with a dye imbibition process. Coloring processes, as illustrated in Konishiroku EP Publication 0.068,9003 and DE No. 3,233,555, are similar to the ink jet procedures of the '154 patent with the exception that there is used in the latter a performed polyurethane latex. In contrast to the prior art teachings, the process of the present ivnention enables a process that generates polymer solution droplets with a dye present during the emulsification step with subsequent particle formation resulting during solvent removal, a one step process, rather than the two steps of the prior art.
While the above compositions and process are suitable for their intended purposes, there continues to be a need for new jet ink processes. Additionally, there continues to be a need for improved processes for ink jet compositions with superior optical print densities, excellent waterfastness characteristics, and reduced wicking properties. Moreover, there continues to be a need for methods of obtaining ink jet compositions wherein the oil soluble dye selected is entrained or trapped in a polymeric composition. Further, there is a need for methods of preparing ink jet compositions which are waterfast, have an excellent affinity for paper substrates and superior drying times. Also, in accordance with the present invention there are provided methods of preparation wherein the resulting inks contain therein oil soluble dyes situated in the interior of the ink particles, thus enabling the dye to be chemically protected, and further preventing the dyes from effecting the surface tension of the particles involved. Additionally, when these compositions with colloidal characteristics impinge the paper substrate during jet printing there is immediately precipitated on the fibers ink particles. Accordingly, these particles separate from the colorless suspending fluid rather than undesirably penetrating into the paper. With penetration there occurs the known problem of showthrough, feathering, or chromatographic separation of the dye components of soluble inks. Further, it is difficult to prepare waterfast images from water-soluble dyes since the ink jet compositions are complex as they contain additives (1) to prevent oxidation thereof; (2) for fixing and for controlling viscosity of the liquid ink particles; and (3) for controlling the evaporation rate and biological activities thereof. Also, with the processes of the present invention there result ink jet compositions with reduced bleeding characteristics, and particles of a size diameter of, for from example, 0.1 to 0.5 microns. Further, a variety of usable polymers, and dye combinations can be used in the process of the present invention since a dye imbibition step is absent.